Project Summary and Abstract A major obstacle to understanding the link between behavior and neuronal activity is the difficulty of electrophysiologically recording the activity of large neuronal populations without limiting visual access. Electrode arrays directly measure electrical signals and offer significantly greater temporal resolution than optical fluorescence techniques, but the resulting obstruction of optical access limits the ability to pair electrode arrays with optogenetic stimulation and calcium imaging. In order to better pair these tools, a new approach to the neuron-electrode interface is required. We propose to fabricate a high-density array of active graphene devices on a transparent flexible substrate for in vivo applications. This novel design will address critical barriers to progress in the field of in vivo neural recording technology: improved signal strength, high temporal resolution, high sensor density, and improved biocompatibility with the unique aspect of transparency. In the first aim, we will develop a surface graphene electrode array (GEA). Critically, the ease of fabrication will allow us to iterate through slight alterations to the GEA design, such as electrode geometry and the flexibility of the support layer through fractal cuts to optimize its ability to mimic the environment. This biomimetic design will result in higher sensitivity through more intimate contact with cells of interest while minimizing damage for long term recordings. The local signal amplification resulting from the field effect response of graphene will make result in a device with an unprecedented level of biocompatibility and sensitivity. This transparent GEA will first be applied to record the activity of the sensory input to the olfactory bulb, located in glomeruli at the surface of the brain. To validate this array, we will image this sensory input in concert with GEA recording. This will allow us to determine whether the GEA can faithfully recover the spatial pattern of OB glomerular responses. We will then implement this array to map the transfer function between the sensory neuron inputs and the output neurons of the OB. In the second aim, we will insert the GEA deep into the brain and record from granule cells, a population of small interneurons located deep in the brain, which form reciprocal synapses with the output neurons of OB. While recording electrically from granule cells, we will image calcium signals in the output neurons. Comparison of these recordings will elucidate the computations that these neurons perform. Together, these experiments will reveal how information is transformed as it moves between different cell types within a neural circuit. In addition, this work will establish GEAs as a powerful tool for investigating neural circuits.